a. Field of Invention
The invention relates to a method for producing an amorphous material in powder form, in which two, at least partially crystalline starting components in powder form are mechanically alloyed by means of a milling process.
b. Background
One method for producing an amorphous alloy is described, for instance, in the publication "Applied Physics Letters", Vol. 43, No. 1, Dec. 1, 1983, pages 1017 to 1019.
Amorphous materials sometimes called "metallic glasses" or "vitrous metals" have been known for some time (see, for instance, "Zeitschrift und Maschinenbau", Vol. 97, September 1980, No. 9, pages 378 to 385). These materials are generally special alloys which can be produced from at least two predetermined starting elements or compounds also called alloying components, by means of special methods. According to their compositon, these alloys are generally divided into two classes, following the periodic table of the elements:
1. Metal/metalloid systems, where elements such as Fe, Co, Ni, Cr, Mo, Zr, Ti, etc. can be considered as the metals, and B, Si, C, N, P, Ge, etc. as metalloids. PA1 2. Metal/metal systems, in which the first metal element can be taken from the group of the late transition metals such as Fe, Ni, Co, Cu, etc. and the second element from the group of the early transition elements such as Zr, Ti, Nb, etc., or from the group of the rare earths or actinides. PA1 1. a boron component of elemental boron or a boron compound or alloy is admixed to the powders of the starting components, PA1 2. the powder mixture of (1) is subjected to the milling process, where an amorphous alloying component is formed from the starting components with embedded or settled fine particles of the boron component, PA1 3. the powder mixture so produced by the steps of (2) is subjected to an annealing treatment below the crystallization temperature of the amorphous alloying component for diffusing the boron into the amorphous alloy component.
Such amorphous alloys have, instead of a crystalline structure, a glasslike amorphous structure and exhibit a number of extraordinary properties or property combinations such as high wear or corrosion resistance, great hardness and tensile strength with at the same time high ductility, as well as the case may be, special magnetic properties. In addition, microcrystalline materials with interesting properties can be produced by use of the amorphous state (see, for instance, German Patent No. 28 34 425).
A method, known for some time, for the industrial production of new materials is the so-called "mechanical alloying" (see, for instance, "Metallurgical Transactions", Vol 5, August 1974, pages 1929 to 1934, or "Scientific American", Vol. 234, 1976, pages 40 to 48). In this method, powders of the starting elements or compounds of the desired alloy are milled together in a ball mill to form a powder mixture. The milling process is continued until a homogeneous alloy of the participating components have been produced.
It is now known from the publication mentioned above (Applied Physics Letters) to provide this method of mechanical alloying also for the production of amorphous metals of the above-mentioned second class and in particular of transition metal/transition metal systems in powder form. Accordingly, it is possible, for instance, to prepare powders of amorphous NiNb. The properties of amorphous metals prepared by mechanical alloying correspond in general to those which are produced by the melt spinning method (see also, for instance, the mentioned publications "Z. Metallkde." and "E. u. M.") However, the range of concentrations in which the glasslike structure is formed, can be far larger than with the melt spinning method. In addition, the method of mechanical alloying is very cost-effective, and the corresponding powders have a very clean surface and thereby a very high reactivity which is of advantage, for instance, in sintering processes, but also in catalytic applications.
It is, therefore, an object of the present invention to develop a method for producing amorphous metal/metalloid systems which contain boron as the metalloid, using the method of mechanical alloying.